Mediterranean Diet and Breast Cancer

Once again the Mediterranean diet is linked to health benefits - this time a 40% lower incidence of certain types of breast cancer in postmenopausal women. Following a Mediterranean style diet has been linked in earlier studies to various health benefits, such as lower rates of heart disease, lower rates of early death, and certain cancers.

A strength of this study is that so many (62,573) Dutch postmenopausal women were followed for a long time (about 20 years). Their diet was analyzed, especially how closely it matched the Mediterranean diet or not. Since alcohol is a risk factor for breast cancer, and dose-related - it was not included as part of the Mediterranean diet in this study. The study found that following a Mediterranean diet with higher consumption of nuts, fruits, vegetables, and whole grains, appeared to be protective against certain breast cancers - it was associated with a reduced risk ofestrogen receptor–negative (ER-) breast cancers. Unfortunately the researchers did not look at olive oil use in this study, because when it started in 1986, it was not typically used in the Netherlands. However, another good study found extra virgin olive oil to be a protective part (against breast cancer) of the Mediterranean diet. From Medscape:

Closely following a Mediterranean diet in everyday life may significantly reduce the risk for types of breast cancer that are associated with poorer prognoses in postmenopausal women, new research indicates. The traditional Mediterranean diet is characterized by a high intake of plant proteins, whole grains, fish, and monounsaturated fat, as well as moderate alcohol intake and low intake of refined grains, red meat, and sweets, say the study authors, led by Piet A. van den Brandt, PhD, an epidemiologist at the Maastricht University Medical Center in the Netherlands.

The new findings come from 62,573 Dutch women aged 55 to 69 years who provided information on dietary and lifestyle habits in 1986 and have since been followed for more than 20 years....The investigators found that women who most closely adhered to a Mediterranean diet had a 40% reduced risk for estrogen receptor–negative (ER-) breast cancer compared to women who adhered to the diet the least. They found a 39% reduced risk for progesterone receptor–negative (PR-)/ER- disease when comparing these same high- and low-adherence groups. Notably, in these results, the definition of the diet excluded alcohol intake, because the consumption of alcohol is a known risk factor for breast cancer....The authors also report that there were no significant associations with the diet and the risk of ER+ disease or total breast cancer.

Dr van den Brandt also explained that older women, who were the subjects of the new study, are more likely to derive benefit than younger women. "Generally speaking, postmenopausal breast cancer seems somewhat more influenced by environmental factors, such as lifestyle and diet, than premenopausal breast cancer, where genetic factors seem to play a more prominent role," he told Medscape Medical News.

Dr Toledo was the senior author of the only large, randomized trial to date in which postmenopausal women were assigned to a dietary intervention to promote their adherence to the traditional Mediterranean diet (JAMA Intern Med. 2015;175:1752–60). The study found that women with a higher adherence to the diet (supplemented with extra-virgin olive oil) showed a substantial reduction of their risk for breast cancer compared to a control group, as reported by Medscape Medical News.